Off gas firing system



P. VON WIESENTHAL 3,433218 OFF GAS FIRING SYSTEM Sheet March 18, 1969 Filed July 5, 1964 United States Patent C) Claims ABSTRAC'I OF THE DISCLOSURE A stack and seal pot arrangement for use with a CO- fired furnace and especially suited to vent either combustion gases when the furnace is in operation or C when the furnace is shut down. Two wells are formed in the lower portion of the stack, one connected in flow series between the CO-fired unit and the stack and the other between the supply of o gas and the stack. Levels of water are maintained in each of the wells and each well has a shroud projecting downward therein so that heads of water can be maintained thereacross to serve as seals against passage of either combustion gases or vented 0fl5 gas through their respective wells or exit via the stack.

This disclosure relates to firing carbon monoxide in lean concentrations occurring in ofi gas trom hydrocarbon catalytic cracking units. The invention contemplates a stack and seal pot arrangement especially suited to this service.

Commercial CO-iring systems must provide not only for the condition when 0f gas is being fired but also for the condition when the COfiring unit is out of service for maintenance. In the former condtion o gas is fed to the CO-firing unit and combustion products are vented to the atmosphere via a stack. The latter conditions calls for bypassing the CO-firing unit by delivering the oi gas directly to the stack. The present advance accommodates both of these conditions in a particularly facile manner by integrating seal pot construction with fabrication of the stacks lower portion. More particularly wells are provded in the lower portion of the stack and a level of water is maintained in each well. Associated with each of the wells is a shroud which conducts gas below the level of the water so that a head of water can be maintained across the two sides of the shroud. This head of water serves as a seal against passage of the gas under the shroud.

The present arrangement ofiers increased safety, ruggedness, and economy over comparable systems. CO- firing systems are characterized by high temperatures and velocities as well as wide swings in operating condi tions. Seal pots receive especially sore abuse. Here the seal pots are brought into the formidable structural arrangement found at the lower portion of a stack. Housing the seal pots within the stack adds an extra measure of safety in the event of C0 leakage. Further the compatibility of stack and seal pot structures also give rise to savings.

These and other features will appear more fully from the accompanying drawing wherein:

FIGURE I is a schematic illustration of the ofl gas i'iring system here contemplated.

FIGURE 11 is an enlarged elevation view in section of the 1ower portion of the stack, and taken along line 2-2 of FIGURE ]I[.

FIGURE 111 is taken along line 3-3 of FIGURE II.

In principal, the firing arrangement set forth herein is not unlike those in common use throughout the petroleum refining industry. During normal operation feed 1 and exhaust 2 seal pots are open and bypass seal pot 3 is closed so that 0 gas trom catalyst regenerator (not 3,433218 Patented Mar. 18, 1969 shown) is conducted via feed duct 6 to CO-iiring unit 7 wherein it is burned. Usually air and auxiliary uel are introduced to the burning of gas. Heat is recovered from the products of C0 combustion by means of non-contact heat exchange with a process stream in tube coil 8. Products of combustion exit CO-firing unit 7 via exhaust duet 9. These products pass through exhaust seal pot 2 and leave via interior 11 and top opening 12 of stack 13.

When CO-firing unit 7 is out of service feed 1 and exhaust 2 seal pots are closed to prevent off gas from entering C0firing unit 7 either through feed duet 6 or through exhaust duet 9. Bypass seal pot 3 is open so that 0 gas is shunted to the atmosphere via bypass duet 24, interior 11 and top opening 12 of stack 13.

Exhaust 2 and bypass 3 seal pots are formed integrally with lower portion 14 of stack 13. Shell 16 lined with refractory 17 cooperates with wall 18 to define exhaust well 19 and bypass well 21 each open te flow communica tion with top opening 12 via interior 11. Each of the wel1s 19 and 21 are suitable for retaining pools of water 22 and 23 therein.

Bypass seal pot 3 is closed during normal operation. When open this seal pot allows o gas te bypass CO- firing unit 7 by fiowing via bypass duet 24, through bypass port 26, under bypass shroud 27 and into interior 11 for exit via top opening 12 of stack 13. During normal operation of the system water adrntted via line 28 forms bypass pool 23 defining level 29 which forms a lquid seal against the flow of gases under bypass shroud 27 from bypass duet 24.

Considering exhaust seal pot 2 in detail, flow through exhaust duet 9 can be either from COfiring unit 7 through exhaust port 31 under exhaust shroud 32 through interior 11 and out top opening 12 of stack 13 or convcrsely from interior 11 of stack 13 under exhaust shroud 32 through exhaust duct 9 back to CO-firing unit 7. Exhaust seal pot 2 is usually called upon during periods when CO- firing unit 7 is out of service to prevent back flow of off gas from interior 11 of stack 13 to CO-firing unit 7. Toward this objective water is introduced via line 33 to maintain level 34 shown as a dashed line.

O gas generally comes from catalyst regenerators at temperatures from 800 to 1100 F. Further, carbon monoxide is quite lethal. S0 when CO-firing unit 7 is to be entered for repair werk, it is necessary that both feed duet 6 and exhaust duet 9 be positively closed. Positive closure is accomplished by means of feed 36 and exhaust '37 guillotine dampers. Feed 1 and exhaust 2 seal pots must generally be closed in order for feed 36 and exhaust 37 guillotine dampers to be moved to their closed positons.

It will -be apparent to these skilled in CO-firing systems that wide devations can be made in the details of this disclosure without departing from the main theme of invention as set forth in the claims.

What is claimed is:

1. A system for iiring off gas from the catalyst regenerator of a hydrocarbon catalytic cracking unit and comprising in combination a feed duet which connects in flow series with the catalyst regenerator to receive the off gas therefrom,

a COfiring unit,

the feed duet connected in flow series with the C0- iring unit to deliver the oi gas thereto,

means operatively associated with the CO-firing unit for reeovering heat from combustion products gen erated therein,

a feed seal means operatively connected in the feed duet to accomplish shutting 0 flow of the 0 gas to the CO-firing unit when the CO-firing unit is not in service,

and to allow passage of the oi gasr the eatalyst regenerator to the CO-firing unit when the CO-firng unit is in service,

a stack with a top opening for venting gases to the atmosphere,

an exhaust duet connectng the CO-firing unit to the stack for exhausting the combustion products there to an exhaust seal means operatively connected in the exhaust duet to accom-plish shutting ofi back flow of gases from the stack to the CO-firing unit when the CO-firing unit is not in service and to allow passage of combustion products from the C-firing unit to the stack when the CO-firing unit is in service,

a bypass duet connecting the feed duet upstream of the feed seal means with the stack,

a bypass seal means operatively connected in the bypass duet for allowing the bypassing of 0 gas to the stack when the CO-firing unit is not in service and to preve1it passage of the ofl gas from the catalys t regenerator directly to the stack when the CO-firing unit is in service,

the stack having a shell with a lower portion,

a wal! connected across the lower portion of the shell to define an exhaust well and a bypass well each open to flow communication with the top opening and each suitable for. retaining a pool of watertherein,

the lower portiorr of the shell defining an exhaust port haust port and havihg an e xhaust lower er r tr t which projects below the exhaustport so that when the level of water in the exhaustwell is above the exhaust lower extenta headpf water may be maintained across the exhaust shroud;

the lowerportion of tlie shell dfining a bypass port throug h which it communicaties in flow series with the bypassduct to receive "o gas therefrom,

the bypass seal means including means for introducing water into the bypass well,l

a bypass shroud connected-tothe shell about the bypassport and having a bypass lower extent which projects below the bypass port so that when the level of water in the bypass well is.above the bypass lower extent a head of water may bemaintained across the bypass shroud 2. The systern Ofclaim 1 with a feed guillotine damper operatively connected to the feed duct downstrearn ofthe bypass duct for positively closing the feed duet,

and an exhaust guillotine damper operatively con nected to the exhaust duet for positive closure there- References"lcited UNITED STATES.PATENTS 2,971,605 2/ 1961 Frost et al.

3248,178 4/1966 H( Jskinsoti.. 3,251,656 5/1966 Edwarcls.

J()SEPH SCOVRONEK, Pfz'rndry Eiraminer. 

